Electron tube apparatus



4 Sheets-Sheet 1 IN V EN TOR. Dona/d H. Pre isf' 'TTOR NE Y Jan. 6, 1959 D. H. PRElsT ELECTRON TUBE APPARATUS Filed Dec. 14, 195s S.: E @u Jan. 6, 1959 D. H. PRElsT 2,857,746

l ELECTRON TUBE APPARATUS Filed Dec. 14, 1953 4 Sheets-Sheet 2 INVENTOR. 0mm/a H. Pre/'57*L ATTORNEY Jan. 6, 1959 D. H. PRElsT 2,867,746

ELECTRON TUBE APPARATUS Filed DSC. 14, 1953 {Sheets-Sheet 3 IN VEN TOR.

Dona/d H. Pre/'57" IJ 9 4 BY 5% ATTN/V5 D. H. PREIST ELECTRON TUBE APPARATUS Jan. 6, 1959 4 Sheets-Sheetl 4 Filed Deo. 14, 1953 :Llivll INVENTOR. Dona/a H. Pre/'s1' [WM ATTDENE Y nited States Patent ilice Patented Jan. 6, 1959 ELECTRON TUBE APPARATUS `Donald H. Preist, Mill Valley, Calif., assignor to Eitel- McCullough, Inc., San Bruno, Calif., a corporation of California Application December 14, 1953, Serial No. 397,977

8 Claims. (Cl. 315-5.35)

My invention relates to electron tubes of the beam type, and more particularly to tubes having cavity resonators such as klystrons.

It is among the objects of my invention to provide improved magnetic beam control means for directing and guiding the electron beam along the axis of the tube.

Another object is to accomplish the above in a practical manner by the provision of a main magnetic circuit for directing the electron beam in a path axially of the tube, and by the provision of a magnetic lens adjacent the gun for guiding the electron beam axially into the field of the main magnetic circuit.

A further object is to provide a tube structure which -is conveniently adaptable for coaction with my improved magnetic means.

Another important object of my invention is to proyvide a tube having portions of the cavity resonators" arranged external to the evacuated envelope, which resonator extensions are constructed and mounted in an improved manner with respect to the tube envelope.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be set forth in the following description of my invention. It is to be understood that I do not limit myself to this disclosure of species of my invention, as I may adopt variant embodiments thereof within the scope of the claims.

Referringv to the drawings:

Figure l is an axial sectional view of a three-cavity klystron embodying the improvements of my invention.

Figure 2 is a side view, partly in section and partly in elevation, showing the tube in conjunction with the external resonator structures and the magnetic circuit Avmeans.

Figure 3 is a transverse sectional view taken in the l plane indicated by line 3-3 of Figure 2, showing the end of the main magnetic circuit; and,

Figure 4 is a similar view taken in plane 4-4 of Figure 2, showing an end of the magnetic lens.

Figure 5 is a transverse sectional view taken in a plane indicated by line 5 5 of Figure 2, looking down on a coil `of the main magnetic circuit and showing a plan 4view of one of the external resonator structures.

In greater detail, and referring to the drawings, Figure l shows my improved tube apart from external portions of the apparatus. The tube illustrated is a threecavity klystron, it being understood that fewer or more cavity resonators may be incorporated without departing from the principles underlying my invention. As reduced to practice, the tube shown is a power amplier operable .in the U. H. F. region and is several feet in overall length, :being capable of delivering more than ten kilowatts C. W. .of R. F. power at frequencies up to 900 megacycles.

In its preferred form the klystron comprises an elon- :gated generally eylindricall envelope having an electron :gun structure 2 at one end and a collector electrode as- ;sembly 3 at the 'other end. The electron beam from the gun to the collector passes through a drift tube made up of metal sections 4, 6, 7, and 8 extending axially of the envelope and having gaps 9, 11 and 12 therebetween. These drift tube sections are preferably of copper. The gaps are bridged by cavity resonator portions generally designated at 13, 14 and 16.

Electron gun 2 comprises a cathode 17 housed in va cup-shaped anode 18. This anode is of a non-magnetic material, preferably copper, and has an aperture 19 coaxially aligned with the cathode. The electrons from the cathode are initially focused through the anode aperture into the drift tube by a suitable focusing electrode 21 in accordance with wellknown electron gun design principles. Cathode 17 may be of any conventional electron emitting material and is heated by a suitable filament or heater (not shown). The entire cathode and focusing electrode assembly is mounted on a stem 22 at the end of the envelope providing terminals for the several component parts of the cathode structure. The stern is sealed to the base of anode 18 at brazed joint 23.

Collector 3 at the opposite end of the envelope comprises a cup-shaped electrode 24, say of copper, connected to drift tube section 8 by an insulating wall of glass 26 sealed between flanges 27. The collector is cooled by a water jacket 28 having inlet and outlet connections 29 and 31, a tubular projection 32 being provided for directing the inlet water along the surface of the collector. A metal tubulation 33 is also provided on the end of the collector, through which the envelope is evacuated. After exhaust the tubulation is pinched off at 34.

The above described elements of the electron tube function in a manner well known for klystron tubes of this type, namely, an electron beam from gun 2 is accelerated by a positive potential on anode 18 and passes through the drift tube, past the interaction spaces provided by gaps 9, 11, and 12, and iinally terminates on collector electrode 24. The three cavity resonator portions 13, 14, and 16 coacting with external extensions and the interaction spaces provided by gaps 9, 11, and 12 serve as the frequency determining elements of the device. In the tube illustrated, which functions as an amplifier, the input signal for modulating the electron beam is fed into the rst resonator portion 13 and the radio-frequency output is taken from the third cavity resonator portion 16, in accordance with the usual manner for three-cavity klystrons.

My tube is of the externally tunable type having the central portions 13, 14 and 16 of the resonators structurally integral with the evacuated envelope and having extensions of such resonators external to the envelope. This simplifies the tube structure and places the mechanical tuning devices outside the vacuum. Figure l shows only those inner portions of the resonators which form part of the tube envelope.

Continuing with the description of Figure l, the drift tube sections 4, 6, 7, and 8 are axially aligned and form side walls of the evacuated envelope. Cavity resonator portions 13, 14, and 16 are disposed transversely of the envelope axis and are mounted on the drift tube sections. These resonator portions form additional wall portions of the evacuated envelope; in other words, they provide vacuum-tight walls bridging the gaps between the drift tube sections.

The three resonator portions 13, 14 and 16 which make vup the main body portion of the envelope are preferably all made alike comprising disk-like copper end walls 36 brazed to adjacent drift tube sections at brazes 37. Cylinders 38 of insulating material, preferably of ceramic,

are sealed between the end walls at anges 39 using conraser/,74e j f tion 13. Such neck structure is an important feature of rounding neck sectiony 4 is preferably relatively small to keep this neck portion of the envelope to a minimum diameter for reasons later discussed. All of these water jackets may be eliminated in lower power tubes, but for vtubes of-h-igher ypower it is desirable to provide for some heat dissipation along the drift tube. In larger tubes these jackets also function as mechanical reinforcing members axially of the tube.

Figures 2 to 5 show my electron tube-in conjunction with the external structures, which structures complete the cavity resonators and provide the magnetic beam control means. First considering the magnetic control, Figure 2 best shows the general layout which comprises a main magnetic circuit positioned about the main body portion of the envelope, which magnetic circuit directsA the electron beam along an axial path through the drift tube and the three resonators. This main magnetic circuit includes several coils, preferably two central coils 48 and an end coil 49. The circuit also includes a frame of magnetic material, such as iron, comprising upper and lower end plates 51 and 52 connected by side members 53. As shown in Figure 3, the end plates are preferably generally square with cut-off corners to take the side members 53, thus providing an open frame structure for getting at the tube since the iron frame also serves as a holder for the tube in its operating position.

The tube is preferably inserted collector end downward. To accomplish this the upper plate is apertured to allow passage of the main body of the tube and a split ring 24 is fitted in the enlarged aperture to extend the iron up to the neck of the tube. At the lower end plate a collar 54 projects upwardly to provide a seat for the supporting flange 47 of the envelope. Coil 49 of the main magnetic circuit is positioned about the support collar 54. The other two coils 48 are suspended in spaced relation intermediate the end plates and are supported from the side members by brackets 56. These brackets are held by screws 57 in slots 58 so that coils 48 may be adjusted axially of the tube and relative to each other, which adjustment is desirable when initially lining up the tube.

It is to be noted that the upper iron end plate 51 lies in a plane transversely across the neck section of the tube envelope. The iron plate is thus interposed between the electron gun and the remaining portion of the tube and functions to shield the electron gun from the field of the main magnetic circuit. It is also to be noted that the elongated neck of the envelope projects beyond the shield an appreciable distance. The purpose of this neck and shield arrangement is to permit the gun to initiate and focus the electron ybeam independently of thev main magnetic circuit and to allow the beam thus formed to travel a distance through the neck before the beam enters the main magnetic field. This permits the inclusion of another important feature about to 'be described.

As shown in Figure 2, a magnetic lens 59 is provided about the neck of the tube for guiding the beam axially into the main magnetic field. This is very important in the practical manufacture and operationof klystrons because without this device there is no vassurance that-l the beam will be started ina precise axial direction. Errors come about because of imperfections in the fabrication and assembly of the gun structure and misalignment while sealing the gun into the envelope. Variations in that respect are particularly bad from tube to vtube in mass production. These variations are obviated by my improvements, because the direction of the beam is independently controlled by the lens 59 before the beam enters the main magnetic circuit.

Lens 59 preferably comprises a coil 61 which is of sufficient size to slip over the anode end of the tube to a position encircling the neck of the envelope. A circular frame of magnetic material such as iron is arranged to extend inwardly from the coil toward the tube neck, which frame comprises disk and cup-shaped pieces -62 and 'housing the coil as shown in Figure 2. T he frame is also split (Figure 4) to permit assembly about. theneck of the tube envelope. The lens is preferably supported onI end `plate 51of the main magnetic circuit andy is s-o mounted that it may be adjusted or shifted transversely relative to the axis of the envelope. This is accomplished by flanged supporting posts 64 and screws 66 passing through oversized holes 67 in plate 51. A large diameter washer 65. is associated with each screw to, prevent the nutsfrom passing through the holes 67.

The magnetic alignment procedure is to rst placel the tube in the main magnetic circuit so that the envelope is coaxial with the main coils, ythis being merely a matter of geometrical relationship. Any initial misalignment of the beam is then corrected by simply shifting the lens untilthe beam is brought into registration with the tube axis, the optimum adjustment in this respect being indicated by maximum. beam current transmission through thetube. After this adjustment has been made, the lens is locked in position.

Now-turning to theexternalresonator. extensionsand referring to Figures 1 and 5, l provide box-like metalstructures 68 arranged so that they are supported solely by the envelope of the tube. This is important` because it is desirable to have, such resonator extensions. mounted independently of the magnetic circuit structure. The-boxlike external resonator portions are preferably rectangular in shape and essentially form extensions of the resonator walls 36 of the tube envelope. These boxes have circular openings and are split in half so that they can be opened and assembled in closed position about the envelope. To provide suitable electrical connection, the walls of the external structures about the circular openings are fitted with resilient contact strips 69 which engage the peripheral edges of resonator walls 36. When assembled about the envelope, the two halves of an external resonator portion are locked together in engaged position by hasps 71. Since the contact strips 69 are compressed against the end walls 36, it is seen that the whole external structure is securely held in the assembled operating position.

Tuning means in the external resonator portions-comprise oppositely disposedrectangular plungers 72 slidably engaging the-walls of the box-like structure, each plunger being disposed in a half portion of the resonatorextension. Suitable rods 73 provide means for moving the plungers to adjust the operating frequency.

Coupling to the input and output resonators may be made in any .conventional manner (not-shown) asby coaxial lines with coupling loops or wave guides through iris openings, such transmission lines benig connected'to the side walls of the external resonator-structures.

While I have described thefprincipal function ofthe lens y59, namely, that of guiding the electron beam axially into the main magnetic field, it is to be noted that the lens has a converging action on the beam andtherefore also functions to control the diameter of the electron beam. The amount of'the converging action dependsupon the current flowing in lens coil 61, which current may-be .varied to adjust the.beamdiameter.v This adjustmentxis important to achieve optimum efficiency in tubeperformance.

Another point to be noted isv that the main magnetic circuit, while preferably including an iron frame with end platesA as described, may merely comprise coils encircling the body portion of the tube since such coils alone will function to direct the electron beam in a path axially of the envelope. The elongated neck of the tube maintains the electron gun suiciently removed from the main magnetic circuit so as to isolate the gun from the main ield. In such case, however, it is still preferable to provide some form of iron plate across the neck of the tube to shield the gun structure, which plate may be a simple disk or the like located ahead of the lens.

The end plates 51 and 52 are respectively referred to herein as the upper and lower end plates, primarily for convenience in describing and claiming the relation of the various elements of the assembly. It will, of course, be understood that no limitation of the scope of the invention, nor restriction regarding the position occupied by the tube in the practice of the invention is thereby j intended.

Instead of using electromagnets it is understood that permanent magnets may be employed to form the magnetic circuit, as will be readily appreciated by those skilled directingv an electron beam in a path axially of the envelope, means shielding the electron gun from the iield' of the main magnetic circuit, and a magnetic lens encircling theV envelope axisy between the gun and said shieldingmeans, said magnetic lens being radially movlable relative to the axis of said main magnetic circuit for guiding the electron beam axially into the field of the main magnetic circuit, said shielding means being located between said main magnetic circuit and said gun.

2. In combination an electron tube comprising an elongated evacuated envelope, an electron gun at one end 'of' lsaid envelope and a collector electrode at the other end of said envelope, a main magnetic circuit surrounding a portion of said envelope adjacent said collector elecvtrode, said envelope having an elongated tubular neck fportion of non-magnetic material removedfrom saidl main magnetic circuit and having an open end adjacent the electron gun, a magnetic shield interposed between said main magnetic circuit and said electron gun, said magnetic shield closely surrounding said neck, said electron gun comprising a cathode in the form of a concave disk of larger diameter than said neck facing said open end of said neck, a tubular focusing electrode adjacent said cathode and a tubular accelerating electrode of non-magnetic material adjacent said open end of said neck portion and coaxial therewith, said electron gun being operable to provide a beam of electrons of smaller diameter than said neck and traveling through said neck toward said collector, a magnetic lens encircling said neck between said accelerating electrode and said main magnetic circuit, and means adjustably mounting said lens With respect to the axis of said neck whereby the diameter of said beam of electrons is controlled and said beam is guided through said neck and into the ield of said main magnetic circuit.

3. The combination of a beam-type electron tube having an elongated envelope with magnetic circuitry comprising a main magnetic circuit and a magnetic lens, said main magnetic circuit comprising a pair of apertured endwalls in spaced parallel relation and means connecting the outer peripheries of said endwalls and forming a hollow frame, said endwalls and said connecting means being made of magnetic material, a plurality of coils contained within and mounted on said frame, said coils and said frames being adapted tol produce a magnetic field having lines of force extending along and parallel to the axis of said electron tube when mounted in said frame, said magnetic lens comprising a coil contained within an annular frame of magnetic material, said annular frame having a gap about its inner periphery, said magnetic lens being adapted to provide a magnetic held having inwardly convex lines of force and means adjustably mounting said magnetic lens on an endwall of said frame of said main magnetic circuit whereby the axis of said lens may be adjusted with respect to the axis of said electron tube mounted in said main magnetic circuit. n

4. The combination of a beam-type electron tube, 'a mainmagnetic circuit, and a magnetic lens, said main magnetic circuit comprising al pair of parallel apertured endwalls, means connecting the outer peripheries of said endwalls and forming a hollow frame, said endwalls and said connecting means comprising magnetic material, the aperture in one of said' endwalls being ofl larger diameter whereby it will allow passage of large diameter portions of said electron tube therethrough, a two-piece insert for the aperture of said one endwall, said insert having an aperture formed at the joint between its two pieces, said aperture in the insert being of substantially smaller diameter than the aperture of said one endwall whereby the insert will iit closely about a small diameter portion of said electron tube, a plurality of coils contained within and mounted on said frame, said mag- .'netic lens comprising a coil of larger diameter than the diameter of the aperture in said insert and an annular frame of magnetic material housing said lens coil, said lens frame having a gap about its inner periphery, the

inner periphery of said lens frame being of smaller diameter than the aperture in said one endwall, said lens frame being split along a line passing across its inner periphery whereby it can be assembled across a,small diameter portion of said electron tube and means adjustably mounting said lens frame on said one endwall for radial adjustment of said lens frame relative `to the frame of said main circuit.

5; The combination of a beam-type electron tube, a main magnetic circuit, a magnetic lens, and an external cavity resonator portion; said electron tube comprising coaxial drift tube sections forming sidewalls of an elongated envelope, said drift tube sections being spaced from each other to provide a gap therebetween, an integral cavity resonator portion bridging the gap and forming part of the envelope, said integral resonator portion conipri'sing metal endwalls o-n adjacent drift tube sections and a cylinder of insulating material sealed between said endwalls, an electron gun at one end of said envelope and a collector electrode at the other end of said envelope; said main magnetic circuit comprising a pair of apertured endwalls, means connecting the outer peripheries of said endwalls and forming a hollow frame, said endwalls and said connecting means comprising magnetic material, the aperture in one of said endwalls being of larger diameter whereby it will allow passage of large diameter portions of said electron tube therethrough, a two-piece insert of magnetic material for said aperture of said endwall, said insert having an aperture formed at the joint between its two pieces, said aperture in said insert being of substantially smaller diameter than the aperture in said one endwall whereby the insert will t closely about a small diameter portion of said electron tube, a plurality of coils contained Within and mounted on said frame; said magnetic lens comprising a coil of larger diameter than the diameter of the aperture in said insert and an annular frame of magnetic material housing said lens coil, said lens frame having a gap about its inner periphery, the inner periphery of said lens frame being of smaller diameter than the aperture in said one endwall, said lens frame being split along a line passing across its inner periphery whereby it can be assembled across a small diameter portion of said electron tube and means adjustably mounting said lens frame on said one endwall for radial adjustment of said lens frame relative to the frame of said main magnetic circuit;v and said external cavity resonator portion comprising a split box-like metal structure having an open central portion through which the envelope extends, resilient contacts about said open central portion of said external resonator portions engageable with said endwalls of said integral resonator portions, and means for locking the split portions of the external resonator portion together in engaged position whereby said external resonator portions are mounted independently of the magnetic circuit and are supported solely by said envelopeof said electron tube.

6. In combination a main magnetic circuit and a magnetic lens,v Said main magneticv circuit comprising a pair ofapertured endwalls, means connecting the outer peripheriesy of said` endwalls and forming a hollow frame,

,said endwalls and said connecting means being of magnetic material, a two-piece insert for the aperture of one of said endwalls; said insert having an aperture formed at the joint between its two pieces,y said aperture in theinsert being of substantially smaller diameter than the aperture of saidendwall, a coil contained withinv and mounted on said frame; said magnetic lens comprising a coil of larger diameter than the` diameter of the aperture in said insert` and an annular frame of magnetiematerial housing saidlens coil, said lens frame having a gap about its inner periphery,.the,inner periphery of said lens frame being of smaller diameter than the aperture. in said one endwall,4 saidvlens framev being split along at line passing across its inner periphery whereby it can be assembled about said coil, and means adjustably mounting said lens frame on said one endwall for radial adjustment of said lensA frame relative. to the framel of said'mainmagnetic circuit.

7. In combination a main magnetic circuit and amagnetic lens, said main vmagnetic circuit comprising av pair of apertured endwalls, means connecting the outerperipheries of `said endwalls and forming a hollow frame, said endwalls and said connecting means being of magnetic material, a two-piece insert for the aperture of one of said endwalls, said insert having an aperture formed at the joint between its two pieces, said aperture in the insert being ofA substantially smaller diameter than the aperture of said endwall, a coil contained within and mounted on said frame; said magnetic lens comprising a coil of larger diameter than the diameter of the aperture in said insert and an annular frame of magnetic material housing said lens coil, said lens frame having a gap about its inner periphery, the inner periphery of said lens frame being of smaller diameter than the aperture in said one endwall, said lens frame being split along a first plane passing through said gap and along a second plane perpendicular to said rst plane Wherebyit can be assembled Vabout said coil, and means adjustably mounting said lens frame on said onev endwall for radial adjustment of said'lens frame relative to the Vframe of said main magnetic circuit.

8.,.In combination a klystron comprising an elongated evacuated envelope, Aan electron gun at one end ofV said envelope and a collector electrode at the other end of said envelope, an R. F. interaction means interposed between said gun and the collector, said R. F. interaction means comprising a plurality of drift tube sections spaced from each other to form gaps, cavity resonatorsbridging said gaps, a main magnetic circuit surrounding said R. F. interactionmeans, said envelope having anelongated tubularneck po-rtion of non-magnetic. material interposed between said R. F. interaction meansrandsaid electron gun, a magnetic shield interposed between said main magneticcircuit and said gun and closely surrounding said neck, said electron gun comprisinga cathode in the form of a concave disk of larger diameter than said neck portion facing one end of said neck, a tubular focusing electrode adjacent said cathode and a tubular accelerating electrode of non-magnetic materialA at-tached to said end of said neck portion and coaxial therewith, said electron gun being operable to provide a. beam of electrons of smaller diameter than said neck and traveling through said neck toward said accelerating electrodev and said magnetic shield, and means adjustably mounting. said lens with respect to the axis of said neck wherebyl the diameter of said beams of electrons is controlled and said beam is guided through said neck into -the Vfield of said main magnetic circuit.

References Cited in theile ofthis patent UNITED STATES PATENTS 2,305,884 Litton Dec. 22, 1942 2,568,668 Steers Sept. 18, 1951 2,581,657 Heppner Jan. 8,1952 2,602,148 Pierce July 1, 1952 2,619,611 Norton et al. Nov. 25, 1952 2,629,066 Eitel etal. Feb. 17., 1953 

